U.S. patent application number 14/720537 was filed with the patent office on 2015-09-10 for power management method for station in wireless lan system and station that supports same.
This patent application is currently assigned to LG ELECTRONICS INC.. The applicant listed for this patent is LG ELECTRONICS INC.. Invention is credited to Yong Ho SEOK.
Application Number | 20150257105 14/720537 |
Document ID | / |
Family ID | 43429702 |
Filed Date | 2015-09-10 |
United States Patent
Application |
20150257105 |
Kind Code |
A1 |
SEOK; Yong Ho |
September 10, 2015 |
POWER MANAGEMENT METHOD FOR STATION IN WIRELESS LAN SYSTEM AND
STATION THAT SUPPORTS SAME
Abstract
A power management method of a station in a wireless local area
network (WLAN) system and the station supporting the method are
provided. The method includes: transmitting to an access point (AP)
a power save configuration (PSC) request frame for reporting that
the STA intends to transition to a power save (PS) mode; receiving
from the AP a PSC response frame in response to the PSC request
frame; and after receiving the PSC response frame, entering the PS
mode.
Inventors: |
SEOK; Yong Ho; (Anyang-si,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG ELECTRONICS INC. |
Seoul |
|
KR |
|
|
Assignee: |
LG ELECTRONICS INC.
Seoul
KR
|
Family ID: |
43429702 |
Appl. No.: |
14/720537 |
Filed: |
May 22, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13871875 |
Apr 26, 2013 |
9078209 |
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14720537 |
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13124655 |
Apr 15, 2011 |
8451761 |
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PCT/KR2010/004499 |
Jul 9, 2010 |
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13871875 |
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61224063 |
Jul 9, 2009 |
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Current U.S.
Class: |
370/311 |
Current CPC
Class: |
H04W 88/08 20130101;
H04W 52/02 20130101; Y02D 70/22 20180101; Y02D 70/142 20180101;
Y02D 30/70 20200801; H04W 52/0235 20130101; H04W 84/12
20130101 |
International
Class: |
H04W 52/02 20060101
H04W052/02 |
Claims
1. A method in a wireless local area network, the method performed
by an access point (AP) that functions as a personal basic service
set control point (PCP) and comprising: receiving, from a second
station, an information request frame for requesting a wakeup
schedule of a first station, the information request frame
including a target address indicating an address of the first
station; transmitting, to the second station, an information
response frame including a first wakeup schedule element in
response to the information request frame, wherein, if AP has an
established wakeup schedule with the first station, the first
wakeup schedule element includes information about the establish
wakeup schedule; and transmitting, to the second station, an
unsolicited information response frame when the AP updates the
first station's wakeup schedule with the first station, the
unsolicited information response frame including a second wakeup
schedule element including information about the updated wakeup
schedule of the first station.
2. The method of claim 1, wherein, if the AP does not have the
established wakeup schedule with the first station, a length of the
first wakeup schedule element is set to zero.
3. The method of claim 1, wherein the first wakeup schedule element
includes a start time field and a sleep interval field, the start
time field indicating a start time offset of a next awake beacon
interval, the sleep interval field indicating a time between two
successive awake beacon intervals.
4. The method of claim 3, wherein the awake beacon interval is
defined as a beacon interval during which the first station is in
the awake state for at least some period of time.
5. A device for a wireless local area network, the device
comprising: a transceiver, and a processor operably coupled with
the transceiver and configured to: instruct the transceiver to
receive, from a second station, an information request frame for
requesting a wakeup schedule of a first station, the information
request frame including a target address indicating an address of
the first station; instruct the transceiver to transmit, to the
second station, an information response frame including a first
wakeup schedule element in response to the information request
frame, wherein, if device has an established wakeup schedule with
the first station, the first wakeup schedule element includes
information about the establish wakeup schedule; and instruct the
transceiver to transmit, to the second station, an unsolicited
information response frame when the device updates the first
station's wakeup schedule with the first station, the unsolicited
information response frame including a second wakeup schedule
element including information about the updated wakeup schedule of
the first station.
6. The device of claim 5, wherein, if the device does not have the
established wakeup schedule with the first station, a length of the
first wakeup schedule element is set to zero.
7. The device of claim 5, wherein the first wakeup schedule element
includes a start time field and a sleep interval field, the start
time field indicating a start time offset of a next awake beacon
interval, the sleep interval field indicating a time between two
successive awake beacon intervals.
8. The device of claim 7, wherein the awake beacon interval is
defined as a beacon interval during which the first station is in
the awake state for at least some period of time.
Description
TECHNICAL FIELD
[0001] The present invention relates to wireless communications,
and more particularly, to a power management method of a station in
a wireless local area network (WLAN) system and the station
supporting the method.
BACKGROUND ART
[0002] With the advancement of information communication
technologies, various wireless communication technologies have
recently been developed. Among the wireless communication
technologies, a wireless local area network (WLAN) is a technology
whereby Internet access is possible in a wireless fashion in homes
or businesses or in a region providing a specific service by using
a portable terminal such as a personal digital assistant (PDA), a
laptop computer, a portable multimedia player (PMP), etc.
[0003] Ever since the institute of electrical and electronics
engineers (IEEE) 802, i.e., a standardization organization for WLAN
technologies, was established in February 1980, many
standardization works have been conducted. In the initial WLAN
technology, a frequency of 2.4 GHz was used according to the IEEE
802.11 to support a data rate of 1 to 2 Mbps by using frequency
hopping, spread spectrum, infrared communication, etc. Recently,
the WLAN technology can support a data rate of up to 54 Mbps by
using orthogonal frequency division multiplex (OFDM). In addition,
the IEEE 802.11 is developing or commercializing standards of
various technologies such as quality of service (QoS) improvement,
access point protocol compatibility, security enhancement, radio
resource measurement, wireless access in vehicular environments,
fast roaming, mesh networks, inter-working with external networks,
wireless network management, etc.
[0004] In the IEEE 802.11, the IEEE 802.11b supports a data rate of
up to 11 Mbps by using a frequency band of 2.4 GHz. The IEEE
802.11a commercialized after the IEEE 802.11b uses a frequency band
of 5 GHz instead of the frequency band of 2.4 GHz and thus
significantly reduces influence of interference in comparison with
the very congested frequency band of 2.4 GHz. In addition, the IEEE
802.11a has improved the data rate to up to 54 Mbps by using the
OFDM technology. Disadvantageously, however, the IEEE 802.11a has a
shorter communication distance than the IEEE 802.11b. Similarly to
the IEEE 802.11b, the IEEE 802.11g implements the data rate of up
to 54 Mbps by using the frequency band of 2.4 GHz. Due to its
backward compatibility, the IEEE 802.11g is drawing attention, and
is advantageous over the IEEE 802.11a in terms of the communication
distance.
[0005] The IEEE 802.11n is a technical standard relatively recently
introduced to overcome a limited data rate which has been
considered as a drawback in the WLAN. The IEEE 802.11n is devised
to increase network speed and reliability and to extend an
operational distance of a wireless network. More specifically, the
IEEE 802.11n supports a high throughput (HT), i.e., a data
processing rate of up to 540 Mbps or higher, and is based on a
multiple input and multiple output (MIMO) technique which uses
multiple antennas in both a transmitter and a receiver to minimize
a transmission error and to optimize a data rate. In addition, this
standard may use a coding scheme which transmits several duplicate
copies to increase data reliability and also may use the OFDM to
support a higher data rate.
[0006] A basic access mechanism of an IEEE 802.11 medium access
control (MAC) mechanism is a carrier sense multiple access with
collision avoidance (CSMA/CA) combined with binary exponential
backoff. The CSMA/CA mechanism is also referred to as a distributed
coordinate function (DCF) of the IEEE 802.11 MAC, and basically
employs a "listen before talk" access mechanism. In this type of
access mechanism, a station (STA) listens a wireless channel or
medium before starting transmission. As a result of listening, if
it is sensed that the medium is not in use, a listening STA starts
its transmission. Otherwise, if it is sensed that the medium is in
use, the STA does not start its transmission but enters a delay
period determined by the binary exponential backoff algorithm.
[0007] The CSMA/CA mechanism also includes virtual carrier sensing
in addition to physical carrier sensing in which the STA directly
listens the medium. The virtual carrier sensing is designed to
compensate for a limitation in the physical carrier sensing such as
a hidden node problem. For the virtual carrier sending, the IEEE
802.11 MAC uses a network allocation vector (NAV). The NAV is a
value transmitted by an STA, currently using the medium or having a
right to use the medium, to anther STA to indicate a remaining time
before the medium returns to an available state. Therefore, a value
set to the NAV corresponds to a period reserved for the use of the
medium by an STA transmitting a corresponding frame.
[0008] One of procedures for setting the NAV is a exchange
procedure of a request to send (RTS) frame and a clear to send
(CTS) frame. The RTS frame and the CTS frame include information
capable of delaying frame transmission from receiving STAs by
reporting upcoming frame transmission to the receiving STAs. The
information may be included in a duration filed of the RTS frame
and the CTS frame. After performing the exchange of the RTS frame
and the CTS frame, a source STA transmits a to-be-transmitted frame
to a destination STA.
[0009] The WLAN system does not require a node of a specific point
to access a network, and thus advantageously can support mobility
of the STA. To support the mobility, most STAs operate by using
batteries. However, battery capacity is limited. Accordingly, there
is a need for a method of managing power of an STA by saving power
consumption of the STA so that the STA can operate for a long time
with limited battery capacity while preventing network
accessibility from being impaired due to the limited battery
capacity.
SUMMARY OF INVENTION
Technical Problem
[0010] The present invention provides a power management method
capable of saving power consumption of a station (STA) and also
provides the STA supporting the method.
Technical Solution
[0011] According to an aspect of the present invention, there is
provided a power management method of an STA. The method includes:
transmitting to an access point (AP) a power save configuration
(PSC) request frame for reporting that the STA intends to
transition to a power save (PS) mode; receiving from the AP a PSC
response frame in response to the PSC request frame; and after
receiving the PSC response frame, entering the PS mode.
[0012] In the aforementioned aspect of the present invention, the
PSC request frame may include a wakeup schedule for indicating a
period in which the STA operates in a wakeup state.
[0013] In addition, the PSC request frame may include a power
management (PM) field, and the PM field may be set to 1.
[0014] In addition, the PSC response frame may include a status
code field to indicate that the AP successfully receives the PSC
request frame.
[0015] According to another aspect of the present invention, there
is provided a power management method of an STA. The method
includes: receiving from an AP an information response frame
including a wakeup schedule of a destination STA which is a target
of frame transmission; and transmitting to the destination STA a
data frame according to the wakeup schedule.
[0016] In the aforementioned aspect of the present invention, the
information response frame may be transmitted in response to an
information request frame for requesting transmission of the
information response frame.
[0017] In addition, the information request frame may have a target
address set to a medium access control (MAC) address of the
destination STA, and may include a request information element for
indicating the wakeup schedule of the destination STA.
[0018] In addition, the information response frame may include a
requested information element field, and the requested information
element field may include a wakeup schedule information element of
the destination STA.
[0019] In addition, the wakeup scheduling information element may
include a length field indicating a length of the wakeup schedule
information element, a start time field indicating a start time at
which the destination STA initially operates in a wakeup state in a
beacon interval, and a sleep interval field indicating an interval
of a period in which the plurality of destination STAs existing in
the beacon interval remain in the wakeup state.
[0020] In addition, if the destination STA operates in an active
mode, the length field of the wakeup schedule information element
of the information response frame may be set to 0.
[0021] According to another aspect of the present invention, there
is provided a power management method of an STA, performed by an
AP, in a WLAN system. The method includes: receiving a PSC request
frame including a wakeup schedule of a first STA from the first STA
coupled to the AP and an information response frame from a PBSS
control point (PCP); receiving from a second STA an information
request frame for requesting the wakeup schedule of the first STA;
and transmitting an information response frame including the wakeup
schedule of the first STA in response to the information request
frame.
Advantageous Effects
[0022] An effective power management method of a station (STA)
constituting a wireless local area network (WLAN) system is
provided to save power consumption of the STA.
DESCRIPTION OF DRAWINGS
[0023] FIG. 1 is a schematic view showing an exemplary structure of
a wireless local area network (WLAN) system according to an
embodiment of the present invention.
[0024] FIG. 2 shows a message flow for a power management method of
a station (STA) according to an embodiment of the present
invention.
[0025] FIG. 3 is a diagram showing an exemplary format of a wakeup
schedule element according to an embodiment of the present
invention.
[0026] FIG. 4 shows a message flow for a frame transmission
procedure according to an embodiment of the present invention.
[0027] FIG. 5 shows a message flow for a power management method of
an STA according to another embodiment of the present
invention.
[0028] FIG. 6 is a block diagram showing a wireless apparatus for
implementing an embodiment of the present invention.
MODE FOR INVENTION
[0029] Hereinafter, embodiments of the present invention will be
described in detail with reference to the accompanying
drawings.
[0030] FIG. 1 is a schematic view showing an exemplary structure of
a wireless local area network (WLAN) system according to an
embodiment of the present invention.
[0031] Referring to FIG. 1, the WLAN system includes one or more
basis service sets (BSSs). The BSS is a set of stations (STAs)
which are successfully synchronized to communicate with one
another, and is not a concept indicating a specific region.
[0032] The BSS can be classified into an infrastructure BSS and an
independent BSS (IBSS). The infrastructure BSS is shown in FIG. 1.
Infrastructure BSSs (i.e., BSS1 and BSS2) include one or more STAs
(i.e., STA1, STA3, and STA4), access points (APs) which are STAs
providing a distribution service, and a distribution system (DS)
connecting a plurality of APs (i.e., AP1 and AP2). On the other
hand, the IBSS does not include APs, and thus all STAs are mobile
STAs. In addition, the IBSS constitutes a self-contained network
since access to the DS is not allowed.
[0033] A personal BSS (PBSS) is one type of an IEEE 802.11 LAN
ad-hoc network similar to the IBSS. STAs of the PBSS are directly
connected to each other, and thus can communicate with each other.
However, unlike the IBSS, a PBSS control point (PCP) served as a
coordinator of the BSS is present in the PBSS. The PCP is an STA
served as a coordinator in the PBSS. The PCP takes charge of
transmission of a beacon frame without the aid of other elements,
and allocates a service period and a contention-based period.
[0034] The STA is an arbitrary functional medium including a medium
access control (MAC) and wireless-medium physical layer interface
conforming to the IEEE 802.11 standard, and includes an AP, a PCP,
a non-AP STA, a non-PCP STA in a broad sense. Further, an STA
including a transceiver operating at 60 MHz is referred to as a
millimeter (mm) wave STA (mSTA).
[0035] The STA for wireless communication includes a processor and
a transceiver, and also includes a user interface, a display means,
etc. The processor is a functional unit devised to generate a frame
to be transmitted through a wireless network or to process a frame
received through the wireless network, and performs various
functions to control STAs. The transceiver is functionally
connected to the processor and is a functional unit devised to
transmit and receive a frame for the STAs through the wireless
network.
[0036] Among the STAs, non-AP/non-PCP STA are portable terminals
operated by users. The non-AP/non-PCP STA may be simply referred to
as an STA. The non-AP/non-PCP STA may also be referred to as a
terminal, a wireless transmit/receive unit (WTRU), a user equipment
(UE), a mobile station (MS), a mobile terminal, a mobile subscriber
unit, etc. In the following descriptions, the STA represents the
non AP/non-PCP STA unless otherwise specified.
[0037] The AP (i.e., AP1 and AP2) is a functional entity for
providing access to the DS through a wireless medium for an
associated STA. Although communication between non-AP STAs in an
infrastructure BSS including the AP is performed via the AP in
principle, the non-AP STAs can perform direct communication when a
direct link is set up. In addition to the terminology of an access
point, the AP may also be referred to as a centralized controller,
a base station (BS), a node-B, a base transceiver system (BTS), a
site controller, etc.
[0038] A plurality of infrastructure BSSs can be interconnected by
the use of the DS. An extended service set (ESS) is a plurality of
BSSs connected by the use of the DS. STAs included in the ESS can
communicate with one another. In the same ESS, a non-AP STA can
move from one BSS to another BSS while performing seamless
communication.
[0039] The DS is a mechanism whereby one AP communicates with
another AP. By using the DS, an AP may transmit a frame for STAs
associated with a BSS managed by the AP, or transmit a frame when
any one of the STAs moves to another BSS, or transmit a frame to an
external network such as a wired network. The DS is not necessarily
a network, and has no limitation in its format as long as a
specific distribution service specified in the IEEE 802.11 can be
provided. For example, the DS may be a wireless network such as a
mesh network, or may be a physical construction for interconnecting
APs.
[0040] In one power management method of an STA supporting the IEEE
802.11 standard, a power state of the STA may be chosen from an
awake state and a doze state. The awake state is a state in which
the STA is fully powered to enable all functions including
transmission/reception. The doze state is a state in which the STA
consumes low power by limiting transmission/reception
functions.
[0041] A power management mode of the STA includes an active mode
and a power save (PS) mode. In the active mode, the STA operates in
the awake state. In the PS mode, the STA may optionally transition
between the awake state and the doze state to save power
consumption. When the STA operates in the PS mode, the STA can
enter the awake state any time.
[0042] In the PS mode, the STA can transition between the two
states to minimize power consumption. That is, when the STA does
not transmit/receive data or the like to/from an AP or another STA,
the STA chooses the doze state to minimize power consumption. If
transmission of the data or the like is necessary or if reception
of the data or the like is requested, the STA enters the awake
state to transmit/receive the data or the like and then returns to
the doze state after completion of transmission/reception.
[0043] While operating in the active mode, the STA may transmit to
the AP a frame in which a power management (Pwr Mgt) bit of a frame
control field included in a MAC header of the frame is set to 1,
and thus may report to the AP that the STA transitions to the PS
mode. The AP cannot transmit the frame to the STA operating in the
PS mode. However, the AP can buffer a frame to be transmitted so
that the frame is transmitted at a predetermined time.
[0044] FIG. 2 shows a message flow for a power management method of
an STA according to an embodiment of the present invention.
[0045] A procedure in which a specific STA enters a power save (PS)
mode is shown in FIG. 2. In the example of FIG. 2, before entering
the PS mode, an STA 205 which intends to enter the PS mode
transmits a power save configuration (PSC) request frame 210 to an
AP 200 to report that the STA 205 will enter the PS mode (step
S210).
[0046] Upon receiving the PSC request frame 210, the AP 200
transmits a PSC response frame 220 to the STA 205 as a response
(step S220).
[0047] Upon receiving the PSC response frame 220, the STA 205
enters the PS mode (step S230).
[0048] Table 1 shows an example of information included in a frame
body of the PSC request frame 210.
TABLE-US-00001 TABLE 1 Order Information 1 Category 2 Action 3
Power Management (PM) 4 Wakeup Schedule Element
[0049] The PSC request frame 210 includes a category field, an
action field, and a power management (PM) field, and optionally
includes a wakeup schedule element field. Herein, the field name or
order is shown for exemplary purposes, and thus a new field may be
added or the order may be modified if necessary.
[0050] The category field and the action field briefly show a
category and action of a specific frame. That is, these fields may
indicate that the frame is related to PSC and is a control signal
for requesting the PSC. An action field value of the PSC request
frame may be set to 2.
[0051] The PM field indicates a specific mode to which the STA
transmitting the PSC request frame intends to transition. The STA
intending to enter the PS mode transmits to the AP the PSC request
frame by setting the PM field value of the PSC request frame to 1.
When the STA operating in the PS mode intends to enter the active
mode, the PM field value of the PSC frame may be set to 0. The PM
field may have a length of one octet.
[0052] Since the example of FIG. 2 shows a case where the STA 205
intends to enter the PS mode while operating in the active mode,
the PM field value of the PSC request frame 210 transmitted by the
STA 205 to the AP 200 is set to 1.
[0053] The wakeup schedule element field contains a wakeup schedule
of the STA transmitting the PSC request frame. If the PSC request
frame is transmitted by including the wakeup schedule element
field, the AP can obtain the wakeup schedule of the STA
transmitting the PSC request frame by using the wakeup schedule
element field. The AP may report the wakeup schedule of the STA to
another STA which requires the wakeup schedule of the STA. A
detailed procedure related thereto will be described below in
greater detail according to other embodiments.
[0054] FIG. 3 is a diagram showing an exemplary format of a wakeup
schedule information element (IE) according to an embodiment of the
present invention.
[0055] A wakeup schedule IE 300 includes an element identifier (ID)
field 310, a length field 320, a start time field 330, and a sleep
interval field 340.
[0056] The element ID field 310 includes information for
identifying an information element. The length field 320 indicates
a length of the wakeup schedule IE.
[0057] The start time field 330 indicates a start time at which an
STA initially operates in the awake state in a beacon interval
(BI). While operating in a PS mode, the STA can repetitively
transition between the awake state and the doze state. If a period
in which the STA operates in the awake state in the BI is defined
as an awake BI (A-BI), the start time field 330 may indicate a
first A-BI start time.
[0058] The sleep interval field 340 indicates a period in which the
STA is in the awake state and which may exist in plural number in
the BI, that is, indicates an interval of the aforementioned A-BI
interval.
[0059] In the example of FIG. 2, the AP 200 can know a period in
which the STA 205 operates in the awake state by using the wakeup
schedule element field of the PSC request frame 210 received from
the STA 205. Accordingly, the AP 200 can buffer a frame to be
transmitted to the STA 205 so that the buffered frame is
transmitted when the STA 205 operates in the awake state.
[0060] Table 2 shows an example of information included in a frame
body of the PSC response frame 220.
TABLE-US-00002 TABLE 2 Order Information 1 Category 2 Action 3
Status Code 4 Wakeup Schedule Element
[0061] The PSC response frame 220 includes a category field, an
action field, and a status code field, and optionally includes a
wakeup schedule element field. Herein, the field name or order is
shown for exemplary purposes, and thus a new field may be added or
the order may be modified if necessary.
[0062] The category field and the action field briefly show a
category and action of a specific frame. That is, these fields may
indicate that the frame is related to PSC and is a control signal
for responding to the PSC. An action field value of the PSC
response frame may be set to 3.
[0063] The status code field includes a response of the AP 200 for
the PSC request of the STA transmitting the PSC request frame 210.
The AP may indicate that the AP can successfully enter the PS mode,
or may indicate that a new wakeup schedule is proposed while
rejecting its wakeup schedule proposed by the STA 205.
[0064] The wakeup schedule field includes a wakeup schedule
element. As a format of the wakeup schedule element, a format of
the wakeup schedule element included in the PSC request frame may
be used. The AP 200 may propose a new wakeup schedule for the STA
205 when the PSC request frame 210 transmitted by the STA 205 does
not include the wakeup schedule or when the STA 205 rejects the
wakeup schedule transmitted using the PSC request frame 210.
[0065] FIG. 4 shows a message flow for a frame transmission
procedure according to an embodiment of the present invention.
[0066] A transmission STA 405 intending to transmit a frame to a
destination STA 407 has to know a wakeup schedule of the
destination STA 407 before transmission of the frame. As described
above, when the destination STA 407 is operating in the PS mode,
the transmission STA 405 cannot arbitrarily transmit the frame to
the destination STA 407. When the transmission STA 405 buffers the
frame to be transmitted to the destination STA 407, the
transmission STA 405 transmits an information request frame 410 to
an AP 400 to obtain the wakeup schedule of the destination STA 407
(step S410).
[0067] In response to the information request frame, the AP 400
transmits to the transmission STA 405 an information response frame
420 including wakeup schedule information of the destination STA
407 (step S420).
[0068] The transmission STA 405 obtains the wakeup schedule of the
destination STA 407 from the information response frame 420, and
can transmit a data frame 430 when the destination STA 407 operates
in the awake state (step S430).
[0069] Table 3 shows an example of information included in a frame
body of the information request frame 410.
TABLE-US-00003 TABLE 3 Order Information 1 Category 2 Action 3
Target Address 4 Request Information element
[0070] The information request frame 410 includes a category field,
an action field, a target address field, and a request information
element field. Herein, the field name or order is shown for
exemplary purposes, and thus a new field may be added or the order
may be modified if necessary.
[0071] The category field and the action field briefly show a
category and action of a specific frame. That is, these fields may
indicate that the frame is a management action frame for requesting
the wakeup schedule information. An action field value of the PSC
response frame may be set to 4.
[0072] The target address field includes information indicating the
destination STA 407 of which the wakeup schedule is intended to be
known by the transmission STA 405. The information indicating the
destination STA 407 may be a MAC address or an association ID (AID)
of the destination STA 407.
[0073] The AP 400 may evaluate the target address field to know the
destination STA 407 of which the wakeup schedule is intended to be
known by the transmission STA 405, and may report the wakeup
schedule of the destination STA 407 to the destination STA 407 by
using the information response frame 420. When the target address
field is set to a broadcast address when it is transmitted to the
AP 400, the AP 400 may report the wakeup schedule of all STAs in a
BSS to the transmission STA 405 by using the information response
frame 420.
[0074] The request information element field includes information
indicating an information element requested using the information
request frame 410. In the example of FIG. 4, the request
information element field includes information indicating the
request of the wakeup schedule information element. The request
information element field may be set to an element ID of the wakeup
schedule information element or may be set to an index value
indicating the wakeup schedule information element.
[0075] The information request frame 410 may be transmitted by
further including wakeup schedule information of the transmission
STA 405 or another STA's wakeup schedule information known to the
transmission STA 405.
[0076] The AP may obtain a wakeup schedule from an STA intending to
enter the PS mode as shown in FIG. 2, or may obtain another STA's
wakeup schedule known to an STA transmitting the information
request frame and an STA transmitting the information request frame
by using the information request frame. In addition, the AP may
manage wakeup schedules of all STAs in the BSS according to a
method of regulating the wakeup schedules of the STAs in the BSS by
using a PSC response frame or an information response frame.
[0077] Table 4 shows an example of information included in a frame
body of the information response frame 420.
TABLE-US-00004 TABLE 4 Order Information 1 Category 2 Action 3
Target Address 4 Requested Information element
[0078] The information response frame 420 includes a category
field, an action field, a target address field, and a request
information element field. Herein, the field name or order is shown
for exemplary purposes, and thus a new field may be added or the
order may be modified if necessary.
[0079] The category field and the action field briefly show a
category and action of a specific frame. That is, these fields may
indicate that the frame is a management action frame for responding
to the request of the wakeup schedule information. An action field
value of the PSC response frame may be set to 5.
[0080] The target address field may directly use a value which is
set in the target address field of the information request frame
410. Alternatively, the target address field may include
information indicating a specific STA of which a wakeup schedule
corresponds to a wakeup schedule transmitted using the request
information element field.
[0081] The requested information element field includes an
information element requested using the information request frame
410. In the example of FIG. 4, the requested information element
field is a wakeup schedule information element of an STA indicated
by the target address field. Therefore, the requested information
element field of the information response frame 420 includes the
wakeup schedule of the STA indicated by the target address field.
The format of FIG. 3 may be used as a format of the wakeup schedule
information element.
[0082] The aforementioned descriptions will now be summarized by
taking an example. In the example of FIG. 4, it is assumed that the
transmission STA 405 transmits the information request frame to the
AP 400 to obtain the wakeup schedule of the destination STA 407. In
this case, the target address field of the information request
frame 410 is set to a MAC address of the destination STA 407, and
the request information element field is set to an index value of
the wakeup schedule information element. The information request
frame 410 may further include a wakeup schedule of the transmission
STA 405 and a wakeup schedule of other STA(s) known to the
transmission STA 405.
[0083] The AP 400 transmits the information response frame 420 in
response to the information request frame 410. In this case, the
target address field of the information response frame 420 is set
to the MAC address of the destination STA 407. The requested
information element field includes a wakeup schedule information
element of the destination STA 407. In this case, the format of
FIG. 3 can be used as a format of the wakeup schedule information
element.
[0084] If the destination STA 407 is operating in the active mode,
the information response frame 420 is transmitted by setting a
length field of a wakeup schedule information element to 0. In this
case, the wakeup schedule information element is included in the
requested information element field of the information response
frame 420.
[0085] When the wakeup schedule of the destination STA 407 depends
on a conventional wakeup schedule, if the destination STA 407 is
modified before starting an operation in the awake state, the AP
400 may transmit a wakeup schedule of the modified (updated)
destination STA 407 to the transmission STA 405. In this case, the
information response frame transmitted by the AP 400 according to
the modification of the wakeup schedule of the destination STA 407
may be transmitted irrespective of the presence of the request of
the transmission STA 405, that is, may be transmitted in the
absence of the request.
[0086] Although the aforementioned embodiments of FIG. 2 and FIG. 4
have been described by taking an example of an operation between an
STA and an AP in an infrastructure BSS, the present invention is
not limited thereto. Thus, the present invention is equally
applicable to a PBSS. The AP of FIG. 2 and FIG. 4 may be a PCP, and
the STA may be a non-PCP STA or an mSTA.
[0087] FIG. 5 shows a message flow for a power management method of
an STA according to another embodiment of the present
invention.
[0088] Referring to FIG. 5, an STA2 507 exchanges a PSC request
frame and a PSC response frame with a PCP 500 before entering the
PS mode (step S510). Formats and functions of the PSC request frame
and PSC response frame exchanged in this case are the same as those
described in the embodiment of FIG. 2. That is, the STA2 507 may
report to the PCP 500 that the STA2 507 intends to enter the PS
mode, and may also transmit its wakeup schedule by using the PSC
request frame. Upon receiving the PSC response frame as an
acknowledgement response from the PCP 500, the STA2 507 may enter
the PS mode.
[0089] In this case, an STA1 505 intending to transmit a data frame
to the STA2 507 exchanges an information request frame and an
information response frame to obtain a wakeup schedule of the STA2
507 (step S520). Formats and functions of the information request
frame and information response frame exchanged in this case are the
same as those described in the embodiment of FIG. 4.
[0090] Upon recognizing the wakeup schedule of the STA2 507, the
STA1 505 transmits a traffic indication message to the STA2 507 to
report that the STA1 505 has a frame to be transmitted (step
S530).
[0091] Upon receiving the traffic indication message, the STA2 507
receives the frame in the active mode (step S540). Alternatively,
instead of entering the doze state, the STA2 507 remains in the
awake state in the PS mode and thus waits to receive a frame to be
transmitted later by the STA1 505. Thereafter, the STA1 505
transmits a data frame to the STA2 507 remaining in the awake state
(in the active mode or the PS mode) (steps S550 and S560). In this
case, a Pwr Mgt bit included in a frame control field of a MAC
header of the transmitted data frame may be set to either 0 or 1
when the data frame is transmitted. Herein, the MAC header format
and a detailed function of the Pwr Mgt bit may be found in the
clauses 7.1.2 and 7.1.3.1 of IEEE Std 802.11.TM.-2007 (Revision of
IEEE Std 802.11-1999) document introduced in Jun. 12, 2007.
[0092] When the STA1 505 intends to report that the STA1 505 will
enter the PS mode, the STA1 505 may transmit the data frame by
setting the Pwr Mgt bit to 1. When the STA1 505 intends to report
that the STA1 505 will operate in the active mode, the STA1 505 may
transmit the data frame by setting the Pwr Mgt bit to 0.
[0093] When the STA1 505 transmits to the STA2 507 the data frame
in which the Pwr Mgt bit is set to 1 (step S560), the STA1 505 can
enter the PS mode after completing the transmission (step
S570).
[0094] Thereafter, when the STA2 507 intends to change a power
management mode or modify a wakeup schedule, the PSC request frame
may be transmitted to the PCP 500 (step S580). The PCP 500 may
transmit a non-requested information response frame to the STA1 505
irrespective of the request of the STA1 505 in order to report the
modification of the wakeup schedule of the STA2 507 to the STA1 505
(step S590).
[0095] Meanwhile, one or more contention based periods (CBPs) may
be present in one beacon interval. An ad-hoc traffic indication
message (ATIM) window may exist in a first CBP, and may begin from
a start of the first CBP. Herein, the ATIM window is a specific
period defined by an ATIM window parameter included in a beacon
frame. An ATIM frame and a control frame have to be transmitted
only during the ATIM window. Details of the ATIM window parameter
and the ATIM frame may be found in the clauses 7.3.27 and 7.2.3.2
of IEEE Std 802.11.TM.-2007 (Revision of IEEE Std 802.11-1999)
document introduced in Jun. 12, 2007.
[0096] An mSTA operating in the PS mode has to operate in the awake
state during an ATIM window in an A-BI.
[0097] A MAC service data unit (MSDU) of which a recipient address
is set to a group address and an MSDU which is transmitted for a
power-conserving STA that can operate in the PS mode are first
reported by using an ATIM frame during the ATIM window. The STA
operating in the PS mode has to listen a report received using the
ATIM frame in order to determine whether the STA needs to remain in
the awake state. If no report is received during the ATIM window,
the mSTA operating in the PS mode in the CBP may enter the doze
state at the end of the ATIM window.
[0098] If the STA receives a directed ATIM frame during the ATIM
window, the STA has to transmit an acknowledgement response for the
reception of the ATIM frame and maintain the awake state to receive
an MSDU to be transmitted to the STA. If the STA transmits the ATIM
frame during the ATIM window and does not receive the ATIM frame
from another STA, the STA may transmit an MPDU in which a PM bit is
set to 1 to another STA receiving the ATIM frame transmitted from
the STA.
[0099] FIG. 6 is a block diagram showing a wireless apparatus for
implementing an embodiment of the present invention. A wireless
apparatus 600 may be an AP, a PCP, or a non-AP/non-PCP STA.
[0100] The wireless apparatus 600 includes a processor 610, a
memory 620, and a transceiver 630. The transceiver 630
transmits/receives a radio signal, and implements an IEEE 802.11
physical layer. The processor 610 is coupled to the transceiver
630, and implements an IEEE 802.11 MAC layer. When the processor
610 processes an operation of the AP/PCP in the aforementioned
methods, the wireless apparatus 600 is the AP/PCP. When the
processor 610 processes an operation of the non-AP/non-PCP in the
aforementioned methods, the wireless apparatus 600 is the
non-AP/non-PCP. The processor 610 and the transceiver 630 may
include an application-specific integrated circuit (ASIC), a
separate chipset, a logic circuit, and/or a data processing unit.
The memory 620 may include a read-only memory (ROM), a random
access memory (RAM), a flash memory, a memory card, a storage
medium, and/or other equivalent storage devices. When the
embodiment of the present invention is implemented in software, the
aforementioned methods can be implemented with a module (i.e.,
process, function, etc.) for performing the aforementioned
functions. The module may be stored in the memory 620 and may be
performed by the processor 610. The memory 620 may be located
inside or outside the processor 610, and may be coupled to the
processor 610 by using various well-known means.
[0101] The aforementioned embodiments include various exemplary
aspects. Although all possible combinations for representing the
various aspects cannot be described, it will be understood by those
skilled in the art that other combinations are also possible.
Therefore, all replacements, modifications and changes should fall
within the spirit and scope of the claims of the present
invention.
* * * * *